New DBAction for creating index concurrently

[kvch]

Relates to #742

[github-actions]

Merging this branch will increase overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/xataio/pgroll/pkg/migrations	75.37% (+0.08%)	👍

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Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/xataio/pgroll/pkg/migrations/dbactions.go	87.22% (-1.59%)	180 (+28)	157 (+22)	23 (+6)	👎
github.com/xataio/pgroll/pkg/migrations/op_create_index.go	67.50% (-1.85%)	40 (-22)	27 (-16)	13 (-6)	👎

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.